1. Field of Invention
The invention relates to an inductor, and, in particular, to an inductor capable of filtering out a common-mode noise and a differential-mode noise simultaneously.
2. Related Art
Because a circuit used in an electronic apparatus, such as a power supply or a power transformer, frequently operates in a high-frequency switching environment, the electro-magnetic element interference (EMI) tends to occur and thus influences the operation of the electronic apparatus. The EMI can be classified into the radiated EMI and the conducted EMI according to a transfer method. The radiated EMI is directly transferred in an open space, while the conducted EMI is transferred through wires.
The conducted EMI may be classified into a common-mode noise and a differential-mode noise according to a conducting path of a noise current. The differential-mode noise occurs when two wires have opposite current flowing directions, and the common-mode noise occurs when all the wires have the same current flowing direction.
In order to eliminate the EMI effectively, an inductor for eliminating the type of the noise is correspondingly disposed in the electronic apparatus according to the type of the noise to be eliminated. For example, if the common-mode noise is to be eliminated, the inductor capable of eliminating the common-mode noise is necessary to dispose in the electronic apparatus. If the differential-mode noise is to be eliminated simultaneously, an additional inductor is need to disposed in the electronic apparatus for eliminating the differential-mode noise. However, this method needs to add inductors, thereby wasting the space in the electronic apparatus, disabling the electronic apparatus from being miniaturized, and increasing the manufacturing cost due to the numerous elements used.
In order to solve the above-mentioned problems, there is provided a conventional inductor 1 including a magnetic element bobbin 11, a primary winding 12, a secondary winding 13, an core set 14 and a frame 15, as shown in FIGS. 1 and 2. The primary winding 12 and the secondary winding 13 are respectively wound around two sides of the magnetic element bobbin 11. The core set 14 is composed of two cores 14a and 14b. First ends of the cores 14a and 14b oppositely pass through the magnetic element bobbin 11, the primary winding 12 and the secondary winding 13. Second ends of the cores 14a and 14b are connected to each other outside the magnetic element bobbin 11. The frame 15 fixes the core set 14. The inductor 1 has the property of the common-mode inductor according to the magnetic element property of the magnetic element bobbin 11 and the cooperation of the magnetic element bobbin 11, the primary winding 12, the secondary winding 13 and the core set 14. In addition, the property of the differential-mode inductor is obtained because the lines of magnetic element forces of the primary winding 12 and the secondary winding 13 are parallel to each other. Although the inductor 1 can eliminate the electromagnetic element interference, the manufacturing cost is relatively increased because it is difficult to shape the magnetic element material into the bobbin in terms of the shaping technology.
Therefore, it is an important subject to provide an inductor, which is capable of filtering out the common-mode noise and the differential-mode noise simultaneously, and can be integrated into one single device in order to facilitate the miniaturization of the device and increase the degree of freedom in the circuit design.